1. Field of the Invention
This invention relates to a control system for a gas turbine aeroengine.
2. Description of the Related Art
Safety is the top priority in an aircraft engine. Therefore, as taught by U.S. Pat. No. 4,716,531, for example, an aircraft engine is equipped with dual (two-channel) control systems and each control system is provided with a monitor system. If the active control system should fail, the other control system takes over control. This system configuration is required by aviation laws and regulations.
Such control systems today utilize an electronic control unit equipped with CPUs (central processing units). Failure detection is particularly difficult with regard to the CPUs among the various unit components. The aforesaid prior art system detects CPU failure by use of a WDT (watchdog timer) circuit and is therefore not adequate regarding failure detection accuracy. An overspeed protector has to be separately installed to make up for this deficiency.
CPU failure detection accuracy can be upgraded by using two or more additionally installed CPUs for monitoring. However, when this configuration is simply applied to a dual system, a total of at least four CPUs is required. The configuration therefore becomes complex and disadvantageous from the aspects of size and cost.
An object of this invention is therefore to overcome the problems of the prior art by providing a control system for a gas turbine aeroengine that achieves a dual control system with an electronic control unit using CPUs, enhances CPU failure detection with a relatively simple configuration, and eliminates the need for provision of an overspeed protector.
For realizing this object, the present invention provides a system for controlling a gas turbine aeroengine having at least a turbine which is rotated by gas produced by the engine to rotate a rotor that sucks in air, having: a first control system including; a speed sensor for detecting a rotational speed of the turbine; operator desired power output detecting means for detecting a desired power output of the engine specified by an operator; first command value calculating means for calculating a first command value based at least on the detected rotational speed of the turbine and the desired power output such that a fuel flow rate to be supplied to the engine is brought to a prescribed value in at least a case when the detected rotational speed of the turbine exceeds a predetermined value, while calculating the first command value at a fuel flow rate needed to bring the detected rotational speed of the turbine to a speed corresponding to the desired power output in at least a case when the detected rotational speed of the turbine does not exceed the predetermined value; fuel supplying means for supplying fuel to the engine based on the calculated command value; and first monitor means for monitoring whether operation of the first command value calculating means is normal. In the system, the first monitor means including: second command value calculating means for calculating a second command value based at least on the detected rotational speed of the turbine and the desired power output such that the fuel flow rate to be supplied to the engine is brought to the prescribed value in at least the case when the detected rotational speed of the turbine exceeds the predetermined value, while calculating the second command value at the fuel flow rate needed to bring the detected rotational speed of the turbine to the speed corresponding to the desired power output in at least the case when the detected rotational speed of the turbine does not exceed the predetermined value; and command value comparing means for comparing the first command value and the second command value with each other and for sending the first command value to the fuel supplying means when the first command value and the second command value coincide completely or at least substantially, the second control system, provided parallel with the first control system, the second control system including:third command value calculating means for calculating a third command value based at least on the detected rotational speed of the turbine and the desired power output such that the fuel flow rate to be supplied to the engine is brought to the prescribed value in at least the case when the detected rotational speed of the turbine exceeds the predetermined value, while calculating the third command value at the fuel flow rate based on the desired power output in at least the case when the detected rotational speed of the turbine does not exceed the predetermined value; and second monitor means for monitoring whether operation of the third command value calculating means is normal and for generating a command value such that the fuel flow rate to be supplied to the engine is brought to the prescribed value when the operation of the third command value calculating means is monitored to be not normal; and the first monitoring means sends the third command value to the fuel supplying means when the operation of the first command value calculating means is monitored to be not normal.